1 62 T. H. MORGAN. 



probable that in Lcptoplana also no better regeneration would 

 occur, even at a pointed end, 1 and if this proves to be the case 

 Schultz's explanation is insufficient. 2 



In my experiments I first examined whether the form of the 

 cut surface at the anterior end had anything to do with the lack 

 of regeneration, for it was possible here, as in the case of Bipa- 

 lium, that the cross-cut surface closed in such a way that subse- 

 quent regeneration was prevented. By changing the form of the 

 cut surface this difficulty should be eliminated. Posterior pieces 

 were cut off through the region of the pharynx and also behind 

 the pharynx. The anterior ends of some of these pieces were 

 very oblique ; others were pointed in the middle, i. e., they were 

 cut off by two oblique cuts meeting in the middle line. In the 

 latter case especially it is impossible that the muscles from the 

 sides could close the anterior cut surface. 3 These pieces were 

 kept alive for two or three weeks, and although it could be seen 

 that there was a little new tissue at the anterior cut surface, yet 

 no further regeneration occurred after the first ten days or there- 

 abouts, and there is no indication that regeneration w r ould have 

 gone any further if the pieces had been kept alive for a greater 

 length of time. 



Sections of these pieces were made. The results will be given 

 below. 



In two other series each worm was cut into three pieces. The 

 head pieces extended to the middle of the region in front of the 

 pharynx. These pieces should be capable of regenerating at the 



1 Loeb says that Thysanozoon regenerates a new head, but he did not determine 

 whether a new brain is formed. Monti also obtained regeneration in this form and 

 also in Leptoplana, except when cut far posteriorly. Lang also records regeneration 

 in marine polyclads. 



2 Schultz states in the opening of his paper that I carried out my experiments 

 without making sections of the planarians, and he intimates that had I done so I 

 would not have reached certain conclusions in regard to the growth of the new part. 

 How Schultz obtained this information it would be interesting to know. Probably 

 he based his generalization on the absence in my earlier papers of reference to histo- 

 logical details with which I was not then especially concerned. As a matter of fact 

 I had made and studied many sections. My students also were at work on the minute 

 anatomy, and one of them published a complete account of the histological changes 

 taking place during regeneration before Schultz's paper appeared. 



3 Whether union of the dorsal and ventral muscles might close these pieces I have 

 not here considered. 



